EP0468239A2 - Process for preparing polydiorganosiloxanes with alkoxy endgroups - Google Patents

Process for preparing polydiorganosiloxanes with alkoxy endgroups Download PDF

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Publication number
EP0468239A2
EP0468239A2 EP91111061A EP91111061A EP0468239A2 EP 0468239 A2 EP0468239 A2 EP 0468239A2 EP 91111061 A EP91111061 A EP 91111061A EP 91111061 A EP91111061 A EP 91111061A EP 0468239 A2 EP0468239 A2 EP 0468239A2
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Prior art keywords
diorganosiloxanes
dihydroxypoly
catalysts
weight
reaction
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German (de)
French (fr)
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EP0468239A3 (en
Inventor
Wilhelm Dr. Weber
Theo Dipl.-Ing. Achtenberg
Karl-Heinz Sockel
Hans Dr. Sattlegger
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Bayer AG
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Bayer AG
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
    • C08G77/04—Polysiloxanes
    • C08G77/06—Preparatory processes
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
    • C08G77/04—Polysiloxanes
    • C08G77/32—Post-polymerisation treatment
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
    • C08G77/04—Polysiloxanes
    • C08G77/14—Polysiloxanes containing silicon bound to oxygen-containing groups
    • C08G77/18—Polysiloxanes containing silicon bound to oxygen-containing groups to alkoxy or aryloxy groups

Definitions

  • the invention relates to the production of poly (diorganosiloxanes) with diorganyloxy-organosilyl or triorganyloxysilyl end groups by reacting a, w-dihydroxy-poly (diorganosiloxanes) with alkoxysilanes in the presence of catalytically active strong alkali metal bases.
  • US Pat. No. 3,161,614 describes the reaction of a, w-dihydroxypoly (diorganosiloxanes) with polyfunctional halosilanes, for example SiC1 4 or CH 3 SiC1 3 .
  • the resulting halogen-containing polysiloxanes are then converted into di- or triorganyloxysilyl-terminated polysiloxanes by alcohols in the presence of acid scavengers.
  • the same patent also mentions the reaction of a-, ⁇ -dihydroxypoly (diorganosiloxanes) with alkoxysilanes in the presence of suitable catalysts, such as amines and metal carboxylates.
  • EP 21 859 and EP 69 256 describe the preparation of RTV-1 K compounds. According to these publications, a, w-dihydroxypoly (diorganosiloxanes) can be reacted with alkoxysilanes in the presence of amines to give the polymers according to the invention.
  • EP 70 786 describes the use of hydroxylamine derivatives instead of amines as catalysts.
  • mixed-functional silanes have become known which, in contrast to pure organyloxy- or organyloxyorganosilanes, can be reacted with a, w-dihydroxypoly- (diorganosiloxanes) without using catalysts to give the polysiloxanes prepared according to the invention.
  • These include alkoxyamidosilanes (DE-PS 1 247 646), alkoxy-oximinosilanes (EP 98 369) and alkoxyacetoxysilanes (US Pat. No. 3,296,195).
  • DE-PS 3 523 206 claims the use of ammonium carbamates, preferably (CH 3 ) 2 NH 2 OCON- (CH 3 ) 2 , as a catalyst for the reaction of OH-terminated polysiloxanes with alkoxysilanes.
  • strong bases as catalysts would actually be obvious. However, such a method has not yet been described. On the contrary, strong bases such as KOH or NaOH were out of the question as catalysts because of the prior art, because they quickly cause undesired rearrangement reactions of the polymer structure.
  • strong bases such as KOH or potassium siloxanolate that branched monoalkoxy-terminated polysiloxanes are formed from tri- or tetraalkoxysilanes and cyclotetra- (dimethylsiloxane) in their presence (US Pat. No. 2,909,549).
  • a, w-dihydroxypoly (dimethylsiloxanes) also react with methyltrimethoxysilane in the presence of KOH.
  • no functional RTV-1K system can be produced from such monoalkoxy-end-stopped polymers, which have, for example, the end group -OSi (CH 3 ) 2 0CH 3 .
  • organyl radicals preferably being methyl radicals.
  • poly (diorganosiloxanes) that contain phenyl groups in addition to methyl groups.
  • R 1 can comprise monovalent alkyl, aryl or alkenyl radicals and R 2 can contain monovalent alkyl radicals.
  • Some of these compounds react with dihydroxypoly (dimethylsiloxanes) (aminoalkylsilanes) even in the absence of catalysts.
  • the process according to the invention can shorten reaction times or lower reaction temperatures, which can bring advantages in the further processing of the products (one-pot process).
  • Strong bases such as alkali metal hydroxides and their silanolates or alcoholates are suitable as catalyst bases. Potassium and sodium compounds are preferred. Tetraalkylammonium hydroxides are also suitable, but have the disadvantage of leaving amine constituents in the polymer. The same applies to alkali amides.
  • the base concentration required for the catalysis is between 0.1 and 100 ppm. It is influenced by whether the polysiloxane contains residues of acidic, basic or buffering constituents which originate from the polymerization process.
  • HCl and HCI-releasing additives such as chlorosilanes, for example (CH 3 ) 3 SiCl, (CH 3 ) 2 SiC1 2 , CH 3 SiCl 3 or SiC1 4, are preferred. It is usually advisable to use the acidic neutralizing agent in excess.
  • the basic and acidic auxiliaries are best introduced in a dilute form which is miscible with the reaction medium.
  • KOH or NaOH can be dissolved in the organyloxysilanes to be reacted, if appropriate with the addition of the corresponding free alcohol.
  • the conditions under which the process according to the invention can be carried out depend on the reactivity of the organyloxysilane used and on the strength of the base used. In most cases the procedure can be carried out at room temperature. The minimum reaction time required for the final stop and the point in time when neutralization must be determined in individual cases. For example, when using KOH and methyltrimethoxysilane, the period between the addition of the base and the neutralizing agent is between 5 and 30 seconds. With NaOH, on the other hand, you have to wait between 5 and 20 minutes. The times also depend on the amount of catalyst used, so that a general determination of the time period for the characterization of the process according to the invention is not possible.
  • the reaction time should be chosen so that the desired end stop has been completed, ie that no SiOH can be detected and that harmful polymer rearrangements do not occur.
  • the latter can be recognized by gel permeation chromatography analysis or by changes in the viscosity of the reaction mixture.
  • the unwanted Polymer rearrangements can be recognized by the fact that with excess alkoxysilane the polymer chain cleaves, which leads to a significant decrease in viscosity.
  • the viscosity and its decrease is naturally influenced by the excess of organyloxysilane. Such an excess is useful in order to complete the reaction as quickly as possible.
  • the excess of alkoxysilane and the alcohol formed as a cleavage product can be removed by neutralization after the strong base has been neutralized.
  • the alkoxysilane excess and the alcohol formed can remain in the polymer in certain formulations.
  • the process can also be carried out as a one-pot process in the mixing unit provided for the production of these compositions.
  • the reactive methoxysilanes are to be used here, the use of Na bases is preferable to the use of potassium compounds because of the longer residence times.
  • fumed silica is preferable to neutralize the base, since it is usually an important component of the mixture anyway.
  • the choice of neutralizing agent can, however, be influenced by the choice of the remaining auxiliaries intended for paste production.
  • test solution 5 parts by weight of a test solution were added to 100 parts by weight of the mixture to be tested.
  • This solution was prepared in the absence of atmospheric moisture by dissolving 20% dibutyltin oxide in tetraethoxysilane at 100 ° C. If there is a rapid increase in viscosity up to gelling after the addition of the test solution, this should be interpreted as an indication of incomplete saturation of the SiOH groups of the OH-terminated polysiloxane. If the gelling fails to materialize and the test mixture hardens from outside to inside when air humidity enters, it can be concluded that the desired end stop, for example -OSi (OCH 3 ) 2 CH 3 , exists.
  • the polymer mixture obtained in Example 1 had a viscosity of 42 Pa * s 24 hours after the preparation.
  • the gel permeation chromatography analysis showed a molecular size distribution which corresponded to that of the OH-terminated poly (dimethylsiloxane) used.
  • the cross-linking test showed no rapid gelling, but gave a fully cured test specimen after 24 hours with the entry of atmospheric moisture with a layer thickness of 2 mm. From these findings it was concluded that the desired implementation had taken place.
  • Example 1 55 parts by weight of the polysiloxane already used in Example 1 were mixed with 2 parts by weight of vinyl triethoxysilane. Then 0.18 part by weight of a solution of 4% potassium hydroxide in methanol was added. After 10 minutes, 0.5 part by weight of a solution of 2.5% H 3 PO 4 in vinyltriethoxysilane was added for neutralization. The mixture had a viscosity of 34.5 pa's and behaved like the mixture from Example 1 in the crosslinking test.
  • the example is intended to show that the process according to the invention can be used to produce a silicone sealant in a "one-pot process".
  • a solution of 0.7% sodium hydroxide and 1% methanol in methyltrimethoxysilane was added to 55 parts by weight of an OH-functional poly (dimethylsiloxane) with a viscosity of 50 pa's.
  • the mixture was then stirred for 10 minutes and then 0.25 part by weight of a solution of 3.4% H 3 PO 4 in methyltrimethoxysilane was added.
  • the paste in tubes was protected from the ingress of atmospheric moisture. After three months, the paste showed no signs of crosslinking when sprayed out, but then hardened to an elastomer under the influence of atmospheric humidity.

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Silicon Polymers (AREA)

Abstract

Die vorliegende Erfindung betrifft ein Verfahren von Triorganyloxysilyl- bzw. Diorganyloxyorganosilyl-endgestoppten Poly(diorganosiloxanen) aus α, ω-Dihydroxypoly(diorganosiloxanen) und Tetraorganyloxysilanen oder Triorganyloxyorganosilanen, wobei man als Katalysatoren stark basische Alkaliverbindungen einsetzt, die man nach dem Ablauf der gewünschten Reaktion und vor dem Eintritt von produktschädigenden Umlagerungsreaktionen neutralisiert.The present invention relates to a process of triorganyloxysilyl- or diorganyloxyorganosilyl-terminated poly (diorganosiloxanes) from α, ω-dihydroxypoly (diorganosiloxanes) and tetraorganyloxysilanes or triorganyloxyorganosilanes, the catalysts and the desired reactions being very basic and the alkali compounds being used neutralized before product-damaging rearrangement reactions occur.

Description

Die Erfindung betrifft die Herstellung von Poly(diorganosiloxanen) mit Diorganyloxy-organosilyl- oder Triorganyloxysilyl-Endgruppen durch Umsetzung von a,w-Dihydroxy-poly(diorganosiloxanen) mit Alkoxysilanen in Gegenwart von katalytisch wirkenden starken Alkalimetallbasen.The invention relates to the production of poly (diorganosiloxanes) with diorganyloxy-organosilyl or triorganyloxysilyl end groups by reacting a, w-dihydroxy-poly (diorganosiloxanes) with alkoxysilanes in the presence of catalytically active strong alkali metal bases.

Es sind bereits mehrere Verfahren zur Herstellung der erfindungsgemäßen Polymere bzw. von solche Polymere enthaltenden Formulierungen bekannt geworden. Die Produkte werden zur Herstellung von 1-Komponenten Siliconpasten verwandt, die in Gegenwart von Feuchtigkeit zu Elastomeren aushärten, im folgenden - RTV-1 K-Massen - genannt.Several processes for producing the polymers according to the invention or formulations containing such polymers have already become known. The products are used for the production of 1-component silicone pastes, which cure in the presence of moisture to form elastomers, hereinafter referred to as RTV-1 K compounds.

In US-PS 3 161 614 wird die Umsetzung von a,w-Dihydroxypoly(diorganosiloxanen) mit mehrfunktionellen Halogensilanen, z.B. SiC14 oder CH3SiC13, beschrieben. Die daraus resultierenden halogenhaltigen Polysiloxane werden dann in Gegenwart von Säurefängern durch Alkohole in Di- oder Triorganyloxysilylendgestoppte Polysiloxane überführt. In der selben Patentschrift wird auch die Umsetzung von a-, ω-Dihydroxypoly(diorganosiloxanen) mit Alkoxysilanen in Gegenwart geeigneter Katalysatoren, wie Amine und Metallcarboxylate, erwähnt.US Pat. No. 3,161,614 describes the reaction of a, w-dihydroxypoly (diorganosiloxanes) with polyfunctional halosilanes, for example SiC1 4 or CH 3 SiC1 3 . The resulting halogen-containing polysiloxanes are then converted into di- or triorganyloxysilyl-terminated polysiloxanes by alcohols in the presence of acid scavengers. The same patent also mentions the reaction of a-, ω-dihydroxypoly (diorganosiloxanes) with alkoxysilanes in the presence of suitable catalysts, such as amines and metal carboxylates.

In EP 21 859 und in EP 69 256 wird die Herstellung von RTV-1 K-Massen beschrieben. Nach diesen Veröffentlichungen können a,w-Dihydroxypoly(diorganosiloxane) in Gegenwart von Aminen mit Alkoxysilanen zu den erfindungsgemäßen Polymeren umgesetzt werden.EP 21 859 and EP 69 256 describe the preparation of RTV-1 K compounds. According to these publications, a, w-dihydroxypoly (diorganosiloxanes) can be reacted with alkoxysilanes in the presence of amines to give the polymers according to the invention.

In EP 70 786 wird die Verwendung von Hydroxylaminderivaten anstelle von Aminen als Katalysatoren beschrieben.EP 70 786 describes the use of hydroxylamine derivatives instead of amines as catalysts.

Weiterhin sind gemischt-funktionelle Silane bekanntgeworden, die mit a,w-Dihydroxypoly-(diorganosiloxanen) im Gegensatz zu reinen Organyloxy- bzw. Organyloxyorganosilanen auch ohne Verwendung von Katalysatoren zu den erfindungsgemäß hergestellten Polysiloxanen umgesetzt werden können. Hierunter fallen Alkoxyamidosilane (DE-PS 1 247 646), Alkoxy-oximinosilane (EP 98 369) und Alkoxyacetoxysilane (US-PS 3 296 195).Furthermore, mixed-functional silanes have become known which, in contrast to pure organyloxy- or organyloxyorganosilanes, can be reacted with a, w-dihydroxypoly- (diorganosiloxanes) without using catalysts to give the polysiloxanes prepared according to the invention. These include alkoxyamidosilanes (DE-PS 1 247 646), alkoxy-oximinosilanes (EP 98 369) and alkoxyacetoxysilanes (US Pat. No. 3,296,195).

In DE-PS 3 523 206 wird die Verwendung von Ammoniumcarbamaten, bevorzugt (CH3)2NH20CON-(CH3)2, als Katalysator für die Umsetzung von OH-endgestoppten Polysiloxanen mit Alkoxysilanen beansprucht.DE-PS 3 523 206 claims the use of ammonium carbamates, preferably (CH 3 ) 2 NH 2 OCON- (CH 3 ) 2 , as a catalyst for the reaction of OH-terminated polysiloxanes with alkoxysilanes.

In der E-PS 137 883werden als Katalysatoren für die gleiche Umsetzung Mischungen aus Aminen und Carbonsäuren beschrieben.In the E-PS 137 883 mixtures of amines and carboxylic acids are described as catalysts for the same reaction.

Alle bisher beschriebenen Verfahren zur Herstellung der genannten Polysiloxane weisen Nachteile auf. Das Verfahren der Umsetzung von a,w-Dihydroxypoly(diorganosiloxanen) mit Halogensilanen mit anschließender Alkoholyse (US-PS 3 161 614) führt zu Polymeren, die korrosiv wirkende Ammoniumsalze enthalten und ist umständlich.All previously described processes for the production of the polysiloxanes mentioned have disadvantages. The process of reacting a, w-dihydroxypoly (diorganosiloxanes) with halosilanes with subsequent alcoholysis (US Pat. No. 3,161,614) leads to polymers which contain corrosive ammonium salts and is cumbersome.

Gemischt funktionelle Alkoxysilane, die neben den Alkoxygruppen einen Amido-, Amino-, Oximino- oder Carboxylatorest tragen, ergeben mit a,w-Dihydroxypoly(diorganosiloxanen) glatt die gewünschten Poly-(diorganosiloxane) mit Triorganyloxysilyl- oder Diorganyloxyorganosilyl-Endgruppen. Die Herstellung der Silane ist jedoch meist kostspielig und die Entfernung der Spaltprodukte macht bei der Herstellung der Formulierungen eigene Verfahrensschritte erforderlich oder ist in der Praxis undurchführbar. Die Entfernung der aus den erwähnten Silanen entstehenden Spaltprodukte wäre aber beispielsweise für die Formulierung von chemisch neutralen, transparenten Polysiloxanmassen wünschenswert. Deshalb ist die Umsetzung von OH-endgestoppten Polysiloxanen mit Alkoxysilanen in Gegenwart geeigneter Katalysatoren vorzuziehen.Mixed functional alkoxysilanes, which carry an amido, amino, oximino or carboxylate residue in addition to the alkoxy groups, give a, w-dihydroxypoly (diorganosiloxanes) smoothly the desired poly- (diorganosiloxanes) with triorganyloxysilyl or diorganyloxyorganosilyl end groups. However, the production of the silanes is usually costly and the removal of the cleavage products necessitates separate process steps in the preparation of the formulations or is impractical in practice. However, the removal of the cleavage products resulting from the silanes mentioned would be desirable, for example, for the formulation of chemically neutral, transparent polysiloxane compositions. It is therefore preferable to react OH-terminated polysiloxanes with alkoxysilanes in the presence of suitable catalysts.

Alle bisher beschriebenen Katalysatoren bzw. Katalysatorsysteme weisen den Nachteil auf, daß sie lange Reaktionszeiten und erhöhte Temperaturen erfordern. Außerdem müssen die Katalysatoren in substantiellen Mengen eingesetzt werden und sind meist nur schwer oder überhaupt nicht aus den Mischungen zu entfernen. Dies trifft zu für Amine, Hydroxylaminderivate und Gemische aus Aminen und Carbonsäuren. Das Verfahren unter Verwendung von Carbamaten, wie (CH3)2NH2OCON(CH3)2, erwies sich zwar als besser geeignet, erfordert aber den Umgang mit substantiellen Mengen an Dimethylamin. Außerdem ist es auf die Endstoppung mit Methoxysilanen beschränkt. Gesucht war also ein Verfahren, das einfach und mit kurzer Reaktionszeit durchgeführt werden kann und das auch auf weniger reaktionsfähige Alkoxysilane, beispielsweise Ethoxysilane, anwendbar ist.All of the catalysts and catalyst systems described so far have the disadvantage that they require long reaction times and elevated temperatures. In addition, the catalysts must be used in substantial amounts and are usually difficult or impossible to remove from the mixtures. This applies to amines, hydroxylamine derivatives and mixtures of amines and carboxylic acids. The method using carbamates, such as (CH 3 ) 2 NH 2 OCON (CH 3 ) 2 , was found to be more suitable, but requires handling substantial amounts of dimethylamine. It is also limited to the end stop with methoxysilanes. What was sought was a process that could be carried out easily and with a short reaction time and that was also applicable to less reactive alkoxysilanes, for example ethoxysilanes.

Die Verwendung starker Basen als Katalysatoren wäre eigentlich naheliegend. Ein solches Verfahren wurde bisher jedoch nicht beschrieben. Starke Basen, wie KOH oder NaOH kamen im Gegenteil nach dem bisherigen Stand der Technik nicht als Katalysatoren in Frage, weil sie rasch unerwünschte Umlagerungsreaktionen des Polymergerüsts herbeiführen. So ist beispielsweise von starken Basen wie KOH oder Kaliumsiloxanolat bekannt, daß in ihrer Gegenwart aus Tri- oder Tetraalkoxysilanen und Cyclotetra-(dimethylsiloxan) verzweigte Monoalkoxy-endgestoppte Polysiloxane entstehen (US-PS 2 909 549). Zu einem solchen Produkt reagieren auch a,w-Dihydroxypoly(dimethylsiloxane) mit Methyltrimethoxysilan in Gegenwart von KOH. Aus derartigen Monoalkoxy-endgestoppten Polymeren, die beispielsweise die Endgruppe -OSi(CH3)20CH3 aufweisen, kann aber kein funktionsfähiges RTV-1 K System hergestellt werden.The use of strong bases as catalysts would actually be obvious. However, such a method has not yet been described. On the contrary, strong bases such as KOH or NaOH were out of the question as catalysts because of the prior art, because they quickly cause undesired rearrangement reactions of the polymer structure. For example, it is known from strong bases such as KOH or potassium siloxanolate that branched monoalkoxy-terminated polysiloxanes are formed from tri- or tetraalkoxysilanes and cyclotetra- (dimethylsiloxane) in their presence (US Pat. No. 2,909,549). For such a product, a, w-dihydroxypoly (dimethylsiloxanes) also react with methyltrimethoxysilane in the presence of KOH. However, no functional RTV-1K system can be produced from such monoalkoxy-end-stopped polymers, which have, for example, the end group -OSi (CH 3 ) 2 0CH 3 .

Überraschend wurde nun ein Verfahren zur Herstellung von Triorganyloxysilyl- bzw. Diorganyloxyorganosilyl-endgestoppten Poly(diorganosiloxanen) aus a,w-Dihydroxypoly(diorganosiloxanen) und Tetraorganyloxysilanen oder Triorganyloxyorganosilanen gefunden, dadurch gekennzeichnet, daß man als Katalysatoren stark basische Alkaliverbindungen einsetzt, die man nach dem Ablauf der gewünschten Reaktion und vor dem Eintritt von produktschädigenden Umlagerungsreaktionen neutralisiert.Surprisingly, a process has now been found for the preparation of triorganyloxysilyl- or diorganyloxyorganosilyl-end-stopped poly (diorganosiloxanes) from a, w-dihydroxypoly (diorganosiloxanes) and tetraorganyloxysilanes or triorganyloxyorganosilanes, characterized in that alkali metal compounds are strongly used as catalysts according to the basic indices Neutralized the course of the desired reaction and before the start of product-damaging rearrangement reactions.

Obwohl die katalytische Wirkung starker Basen auf Gemische aus Polysiloxanen und Alkoxysilanen bekannt war, lag das erfindungsgemäße Verfahren keineswegs nahe. Es konnte nämlich nicht vorhergesagt werden, daß es gelingt, den erwünschten Endstoppungsschritt so durchzuführen, daß nicht bereits die unerwünschte Polymerumlagerung stattfindet.Although the catalytic effect of strong bases on mixtures of polysiloxanes and alkoxysilanes was known, the process according to the invention was by no means obvious. Namely, it could not be predicted that the desired end-stop step could be carried out in such a way that the undesired polymer rearrangement did not already take place.

Für das erfindungsgemäße Verfahren sind alle bekannten a,w-Dihydroxypoly(diorganosiloxane) geeignet, wobei die Organylreste bevorzugt Methylreste sind. Als weiteres Beispiel sollen Poly(diorganosiloxane) genannt werden, die neben Methylgruppen noch Phenylgruppen enthalten.All known a, w-dihydroxypoly (diorganosiloxanes) are suitable for the process according to the invention, the organyl radicals preferably being methyl radicals. Another example is poly (diorganosiloxanes) that contain phenyl groups in addition to methyl groups.

Zur Umsetzung mit den a,w-Dihydroxypoly(diorganosiloxanen) eignen sich Verbindungen folgenden Typs:

Figure imgb0001
wobei der Index m 0 oder 1 sein, R1 einwertige Alkyl-, Aryl- oder Alkenylreste und R2 einwertige Alkylreste umfassen kann. Als Beispiele können genannt werden: Si(OCH3)4, Si(OC2Hs)4, Si[OCH(CH3)2]4, CH3Si-(OCH3)3, CH3Si(OC2H5)3, CH2=CHSi(OC2H5)3, C6H5Si(OCH3)3 und CH3Si[OCH2CH(CH3)2]3. Der Rest R1 kann aber auch funktionelle Gruppen tragen, wie beispielsweise in den Verbindungen XCH2CH2CH2Si(OR2)-3 mit
Figure imgb0002
HS-, H2N-, R2N-, H2NCH2CH2NH- oder CH2 = C(CH3)COO-. Einige dieser Verbindungen reagieren auch schon in Abwesenheit von Katalysatoren mit Dihydroxypoly(dimethylsiloxanen)(Aminoalkylsilane). In solchen Fällen können durch das erfindungsgemäße Verfahren Raktionszeiten verkürzt bzw. Reaktionstemperaturen gesenkt werden, was Vorteile bei der weiteren Verarbeitung der Produkte bringen kann (Eintopfverfahren).Compounds of the following types are suitable for reaction with the a, w-dihydroxypoly (diorganosiloxanes):
Figure imgb0001
 where the index m can be 0 or 1, R 1 can comprise monovalent alkyl, aryl or alkenyl radicals and R 2 can contain monovalent alkyl radicals. Examples include: Si (OCH 3 ) 4 , Si (OC 2 Hs) 4 , Si [OCH (CH 3 ) 2] 4 , CH 3 Si (OCH 3 ) 3 , CH3Si (OC2H5) 3, CH 2 = CHSi (OC 2 H 5 ) 3 , C 6 H 5 Si (OCH 3 ) 3 and CH 3 Si [OCH 2 CH (CH 3 ) 2] 3 . The radical R 1 can, however, also carry functional groups, for example in the compounds XCH 2 CH 2 CH 2 Si (OR 2 ) - 3
Figure imgb0002
 HS-, H 2 N-, R 2 N-, H 2 NCH 2 CH 2 NH- or CH 2 = C (CH 3 ) COO-. Some of these compounds react with dihydroxypoly (dimethylsiloxanes) (aminoalkylsilanes) even in the absence of catalysts. In such cases, the process according to the invention can shorten reaction times or lower reaction temperatures, which can bring advantages in the further processing of the products (one-pot process).

Als Katalysatorbasen eignen sich starke Basen wie Alkalimetallhydroxide und deren Silanolate oder Alkoholate. Bevorzugt sind Kalium- und Natriumverbindungen. Tetraalkylammoniumhydroxide eignen sich ebenfalls, besitzen aber den Nachteil, aminische Bestandteile im Polymer zu hinterlassen. Ähnliches gilt für Alkaliamide. Die für die Katalyse erforderliche Basenkonzentration liegt zwischen 0,1 und 100 ppm. Sie wird davon beeinflußt, ob das Polysiloxan Reste von sauren, basischen oder als Puffer wirkenden Bestandteilen enthält, die aus dem Polymerisationsverfahren stammen.Strong bases such as alkali metal hydroxides and their silanolates or alcoholates are suitable as catalyst bases. Potassium and sodium compounds are preferred. Tetraalkylammonium hydroxides are also suitable, but have the disadvantage of leaving amine constituents in the polymer. The same applies to alkali amides. The base concentration required for the catalysis is between 0.1 and 100 ppm. It is influenced by whether the polysiloxane contains residues of acidic, basic or buffering constituents which originate from the polymerization process.

Zur Neutralisation eignen sich starke und schwache Säuren wie HCI, H2S04, H3P04, Carbonsäuren und C02. Auch pyrogene Kieselsäure kann in Fällen, in denen eine Weiterverarbeitung zu kieselsäurehaltigen Mischungen vorgesehen ist, Verwendung finden. Bevorzugt sind HCI sowie HCI-freisetzende Additive wie Chlorsilane, beispielsweise (CH3)3SiCl, (CH3)2SiC12, CH3SiCl3 oder SiC14. Meist empfiehlt es sich, das saure Neutralisationsmittel im Überschuß zu verwenden.Strong and weak acids such as HCl, H 2 S0 4 , H 3 P0 4 , carboxylic acids and C0 2 are suitable for neutralization. Fumed silica can also be used in cases where further processing into mixtures containing silica is intended. HCl and HCI-releasing additives such as chlorosilanes, for example (CH 3 ) 3 SiCl, (CH 3 ) 2 SiC1 2 , CH 3 SiCl 3 or SiC1 4, are preferred. It is usually advisable to use the acidic neutralizing agent in excess.

Die basischen und sauren Hilfsstoffe bringt man am besten in einer verdünnten, mit dem Reaktionsmedium mischbaren Form ein. So kann beispielsweise KOH bzw. NaOH in den umzusetzenden Organyloxysilanen, gegebenenfalls unter Hinzufügung des entsprechenden freien Alkohols, gelöst werden.The basic and acidic auxiliaries are best introduced in a dilute form which is miscible with the reaction medium. For example, KOH or NaOH can be dissolved in the organyloxysilanes to be reacted, if appropriate with the addition of the corresponding free alcohol.

Die Bedingungen, unter denen das erfindungsgemäße Verfahren durchgeführt werden kann, richten sich nach der Reaktivität des eingesetzten Organyloxysilans und nach der Stärke der eingesetzten Base. In den meisten Fällen kann das Verfahren bei Raumtemperatur ausgeführt werden. Die für die Endstoppung erforderliche Mindestreaktionszeit und der Zeitpunkt, wann neutralisiert werden muß, sind im Einzelfall zu ermitteln. So liegt beispielsweise bei Verwendung von KOH und Methyltrimethoxysilan der Zeitraum zwischen der Zugabe der Base und des Neutralisationsmittels zwischen 5 und 30 Sekunden. Mit NaOH dagegen muß man einen Zeitraum zwischen 5 und 20 Minuten einhalten. Die Zeiten sind außerdem von der verwendeten Katalysatormenge abhängig, so daß eine generelle Festlegung des Zeitraums für die Charakterisierung des erfindungsgemäßen Verfahrens nicht möglich ist. Die Reaktionszeit ist jedoch so zu wählen, daß die gewünschte Endstoppung vollständig erfolgt ist, d.h., daß kein SiOH mehr nachweisbar ist und daß andererseits schädliche Polymerumlagerungen ausbleiben. Letztere erkennt man durch gelpermeationschromatographische Analyse oder an Viskositätsveränderungen der Reaktionsmischung. Die unerwünschten Polymerumlagerungen geben sich nämlich dadurch zu erkennen, daß mit überschüssigem Alkoxysilan eine Spaltung der Polymerkette einsetzt, die zu einer deutlichen Viskositätsabnahme führt. Die Viskosität und deren Abnahme wird naturgemäß durch den Überschuß an Organyloxysilan beeinflußt. Ein solcher Überschuß ist sinnvoll, um die Reaktion möglichst rasch zu vervollständigen. Der Überschuß an Alkoxysilan und der als Spaltprodukt entstehende Alkohol können nach der Neutralisation der starken Base durch Ausheizen entfernt werden. Für bestimmte Einsatzzwecke, beispielsweise in feuchtigkeitshärtenden Silicondichtstoffen, können bei bestimmten Rezepturen der Alkoxysilanüberschuß und der gebildete Alkohol im Polymer verbleiben.The conditions under which the process according to the invention can be carried out depend on the reactivity of the organyloxysilane used and on the strength of the base used. In most cases the procedure can be carried out at room temperature. The minimum reaction time required for the final stop and the point in time when neutralization must be determined in individual cases. For example, when using KOH and methyltrimethoxysilane, the period between the addition of the base and the neutralizing agent is between 5 and 30 seconds. With NaOH, on the other hand, you have to wait between 5 and 20 minutes. The times also depend on the amount of catalyst used, so that a general determination of the time period for the characterization of the process according to the invention is not possible. However, the reaction time should be chosen so that the desired end stop has been completed, ie that no SiOH can be detected and that harmful polymer rearrangements do not occur. The latter can be recognized by gel permeation chromatography analysis or by changes in the viscosity of the reaction mixture. The unwanted Polymer rearrangements can be recognized by the fact that with excess alkoxysilane the polymer chain cleaves, which leads to a significant decrease in viscosity. The viscosity and its decrease is naturally influenced by the excess of organyloxysilane. Such an excess is useful in order to complete the reaction as quickly as possible. The excess of alkoxysilane and the alcohol formed as a cleavage product can be removed by neutralization after the strong base has been neutralized. For certain applications, for example in moisture-curing silicone sealants, the alkoxysilane excess and the alcohol formed can remain in the polymer in certain formulations.

Ist man, wie oben am Beispiel des Einsatzes von Methyltrimethoxysilan und Kaliumhydroxid erläutert, auf die genaue Einhaltung sehr kurzer Verweilzeiten angewiesen, empfiehlt sich eine kontinuierliche Verfahrensführung. Die basischen und sauren Hilfsstoffe können dann beispielsweise mit Hilfe von Dosierpumpen in Statikmischersystemen mit dem Reaktionsmedium vereinigt werden.If, as explained above using the example of the use of methyltrimethoxysilane and potassium hydroxide, you are dependent on the exact observance of very short residence times, a continuous process management is recommended. The basic and acidic auxiliaries can then be combined with the reaction medium, for example with the aid of metering pumps in static mixer systems.

Ist der Einsatz der nach dem erfindungsgemäßen Verfahren hergestellten Polysiloxane in feuchtigkeitshärtenden RTV Massen beabsichtigt, kann das Verfahren auch in dem zur Herstellung dieser Massen vorgesehenen Mischaggregat als Eintopfverfahren durchgeführt werden. Sollen hierbei die reaktionsfähigen Methoxysilane Verwendung finden, ist der Einsatz von Na-Basen wegen der längeren Verweilzeiten gegenüber der Verwendung von Kaliumverbindungen vorzuziehen. Bei der Herstellung von Silicondichtstoffen kann es sinnvoll sein, pyrogene Kieselsäure zur Neutralisation der Base zu verwenden, da sie meist ohnehin einen wichtigen Mischungsbestandteil darstellt. Die Wahl des Neutralisationsmittels kann dabei jedoch von der Wahl der restlichen, zur Pastenherstellung vorgesehenen Hilfsstoffe beeinflußt werden.If the polysiloxanes produced by the process according to the invention are intended to be used in moisture-curing RTV compositions, the process can also be carried out as a one-pot process in the mixing unit provided for the production of these compositions. If the reactive methoxysilanes are to be used here, the use of Na bases is preferable to the use of potassium compounds because of the longer residence times. When manufacturing silicone sealants, it can make sense to use fumed silica to neutralize the base, since it is usually an important component of the mixture anyway. The choice of neutralizing agent can, however, be influenced by the choice of the remaining auxiliaries intended for paste production.

Das erfindungsgemäße Verfahren soll anhand der folgenden Beispiele näher erläutert werden.The process according to the invention will be explained in more detail with the aid of the following examples.

Beispiel 1example 1

In einem Planetenmischer wurde eine Mischung von 55 Gew.-Teilen eines OH-endgestoppten Poly-(dimethylsiloxans), das eine Viskosität von 50 Pa's besaß, mit 1 Gew.-Teil Methyltrimethoxysilan hergestellt. In diese Mischung wurden 0,09 Gew.-Teile einer Katalysatorlösung von 4 % Natriumhydroxid und 1 % Methanol in Methyltrimethoxysilan eingerührt. Zehn Minuten nach der Zugabe des Katalysators wurden 0,73 Gew.-Teile einer Lösung von 1 % Dimethyldichlorsilan in Trimethylsilyl-endgestopptem Poly-(dimethylsiloxan) der Viskosität 0,1 Pa's zugegeben. Danach wurde das Reaktionsgemisch in einem Rotationsverdampfer zwei Stunden bei 140° C und von 25 mbar ausgeheizt.In a planetary mixer, a mixture of 55 parts by weight of an OH-terminated poly- (dimethylsiloxane), which had a viscosity of 50 pa's, was prepared with 1 part by weight of methyltrimethoxysilane. 0.09 part by weight of a catalyst solution of 4% sodium hydroxide and 1% methanol in methyltrimethoxysilane was stirred into this mixture. Ten minutes after the addition of the catalyst, 0.73 parts by weight of a solution of 1% dimethyldichlorosilane in trimethylsilyl-terminated poly (dimethylsiloxane) having a viscosity of 0.1 Pa were added. The reaction mixture was then heated in a rotary evaporator at 140 ° C. and 25 mbar for two hours.

Die resultierende Polymermischung wurde folgendermaßen untersucht:

  • a) Viskositätsbestimmung mit einem Haake Rotationsviskosimeter,
  • b) gelpermeationschromatographische Analyse und
  • c) Vernetzungstest.
The resulting polymer blend was examined as follows:
  • a) determination of viscosity with a Haake rotary viscometer,
  • b) gel permeation chromatography analysis and
  • c) Networking test.

Bei dem unter c) beschriebenen Vernetzungstest wurden 100 Gew.-Teile der zu prüfenden Mischung mit 5 Gew.-Teilen einer Testlösung versetzt. Diese Lösung war unter Ausschluß von Luftfeuchtigkeit durch Auflösen von 20 % Dibutylzinnoxid in Tetraethoxysilan bei 100° C hergestellt worden. Tritt nach der Zugabe der Testlösung ein rascher Viskositätsanstieg bis hin zur Vergelung ein, ist dies als Hinweis auf eine unvollständige Absättigung der SiOH-Gruppen des OH-endgestoppten Polysiloxans zu interpretieren. Bleibt die Vergelung aus und härtet die Testmischung bei Zutritt von Luftfeuchtigkeit von außen nach innen aus, kann auf die Existenz der gewünschten Endstoppung, beispielsweise -OSi(OCH3)2CH3 geschlossen werden. Bleibt aber sowohl die rasche Vergelung wie auch die Aushärtung unter Zutritt von Luftfeuchtigkeit aus, oder entsteht nur langsam ein weicher, dünner Film, ist dies als Beweis dafür anzusehen, daß die unerwünschte Polymerumlagerung stattgefunden hat und verzweigte Polymere mit -OSi(CH3)-20CH3Endgruppen entstanden sind.In the crosslinking test described under c), 5 parts by weight of a test solution were added to 100 parts by weight of the mixture to be tested. This solution was prepared in the absence of atmospheric moisture by dissolving 20% dibutyltin oxide in tetraethoxysilane at 100 ° C. If there is a rapid increase in viscosity up to gelling after the addition of the test solution, this should be interpreted as an indication of incomplete saturation of the SiOH groups of the OH-terminated polysiloxane. If the gelling fails to materialize and the test mixture hardens from outside to inside when air humidity enters, it can be concluded that the desired end stop, for example -OSi (OCH 3 ) 2 CH 3 , exists. However, if both the rapid gelation and the curing do not take place under the influence of atmospheric humidity, or if a soft, thin film only forms slowly, this must be regarded as evidence that the undesired polymer rearrangement has taken place and branched polymers with -OSi (CH 3 ) - 2 0CH 3 end groups have emerged.

Die im Beispiel 1 erzielte Polymermischung besaß 24 Stunden nach der Herstellung eine Viskosität von 42 Pa*s. Die gelpermeationschromatographische Analyse ergab eine Molekülgrößenverteilung, die der des eingesetzten OH-endgestoppten Poly(dimethylsiloxans) entsprach. Der Vernetzungstest zeigte keine rasche Vergelung, sondern ergab nach 24 Stunden unter Zutritt von Luftfeuchtigkeit bei 2 mm Schichtdicke einen vollständig ausgehärteten Prüfling. Aus diesen Befunden wurde geschlossen, daß die gewünschte Umsetzuna

Figure imgb0003
stattgefunden hatte.The polymer mixture obtained in Example 1 had a viscosity of 42 Pa * s 24 hours after the preparation. The gel permeation chromatography analysis showed a molecular size distribution which corresponded to that of the OH-terminated poly (dimethylsiloxane) used. The cross-linking test showed no rapid gelling, but gave a fully cured test specimen after 24 hours with the entry of atmospheric moisture with a layer thickness of 2 mm. From these findings it was concluded that the desired implementation
Figure imgb0003
 had taken place.

Beispiel 2 (Vergleichsbeispiel):

  • Das Beispiel 1 wurde ohne Zugabe von KOH oder Dimethyldichlorsilan wiederholt. Die Mischung hatte eine Viskosität von 43 Pa's und vergelte im Vernetzungstest bereits bei der Zugabe der Testlösung.
Example 2 (comparative example):
  • Example 1 was repeated without the addition of KOH or dimethyldichlorosilane. The mixture had a viscosity of 43 pa's and gelled in the crosslinking test when the test solution was added.

Beispiel 3 (Vergleichsbeispiel):

  • Das Beispiel 1 wurde ohne Zugabe von Dimethyldichlorsilan wiederholt. Die Reaktionsmischung besaß nach 24 Stunden eine Viskosität von 2 Pa*s. Die gelpermeationschromatographische Analyse ergab im Vergleich zu Beispiel 1 eine deutliche Verschiebung des Verteilungsmaximums zu kleinerer Molekülgröße. Im Vernetzungstest trat weder eine rasche Vergelung ein noch erfolgte unter Zutritt von Luftfeuchtigkeit Aushärtung. Nach 24 Stunden hatte sich lediglich eine schwach vernetzte Schicht an der Oberfläche gebildet.
Example 3 (comparative example):
  • Example 1 was repeated without adding dimethyldichlorosilane. After 24 hours, the reaction mixture had a viscosity of 2 Pa * s. The gel permeation chromatography analysis showed in comparison to Example 1 a clear shift in the distribution maximum to a smaller molecule size. In the crosslinking test, rapid gelation did not occur, nor did curing take place under the influence of atmospheric moisture. After 24 hours, only a weakly cross-linked layer had formed on the surface.

Beispiel 4Example 4

55 Gew.-Teile des bereits im Beispiel 1 verwendeten Polysiloxans wurden mit 2 Gew.-Teilen Vinyltriethoxysilan vermischt. Dann wurden 0,18 Gew.-Teile einer Lösung von 4 % Kaliumhydroxid in Methanol zugegeben. Nach 10 Minuten wurden zur Neutralisation 0,5 Gew.-Teile einer Lösung von 2,5 % H3P04 in Vinyltriethoxysilan zugegeben. Die Mischung besaß eine Viskosität von 34,5 Pa's und verhielt sich im Vernetzungstest wie die Mischung aus Beispiel 1.55 parts by weight of the polysiloxane already used in Example 1 were mixed with 2 parts by weight of vinyl triethoxysilane. Then 0.18 part by weight of a solution of 4% potassium hydroxide in methanol was added. After 10 minutes, 0.5 part by weight of a solution of 2.5% H 3 PO 4 in vinyltriethoxysilane was added for neutralization. The mixture had a viscosity of 34.5 pa's and behaved like the mixture from Example 1 in the crosslinking test.

Beispiel 5Example 5

Das Beispiel soll zeigen, daß mit Hilfe des erfindungsgemäßen Verfahrens ein Silicondichtstoffe im "Eintopfverfahren" hergestellt werden kann.The example is intended to show that the process according to the invention can be used to produce a silicone sealant in a "one-pot process".

In einem Planetenmischer wurden zu 55 Gew.-Teilen eines OH-funktionellen Poly(dimethylsiloxans) mit der Viskosität 50 Pa's 0,5 Gew.-Teile einer Lösung von 0,7 % Natriumhydroxid und 1 % Methanol in Methyltrimethoxysilan gegeben. Dann wurde 10 Minuten lang gerührt und anschließend 0,25 Gew.-Teile einer Lösung von 3,4 % H3P04 in Methyltrimethoxysilan hinzugefügt. Dann wurden nacheinander die folgenden Bestandteile zugemischt: 29 Gew.-Teile eines Trimethylsilyl-endgestoppten Poly-(dimethylsiloxans) der Viskosität 0,1 Pa*s, 9,5 Gew.-Teile einer hydrophoben pyrogenen Kieselsäure mit einer spezifischen Oberfläche von 130 m2/g, 0,8 Gew.-Teile eines Silans mit der Formel H2NCH2CH2CH2Si-(OC2H5)3 sowie 0,3 Gew.-Teile einer Katalysatorlösung, bestehend aus 65 % Dibutylzinn-bis-(2-ethylhexa- noat) und 35 % Toluol.In a planetary mixer, 0.5 part by weight of a solution of 0.7% sodium hydroxide and 1% methanol in methyltrimethoxysilane was added to 55 parts by weight of an OH-functional poly (dimethylsiloxane) with a viscosity of 50 pa's. The mixture was then stirred for 10 minutes and then 0.25 part by weight of a solution of 3.4% H 3 PO 4 in methyltrimethoxysilane was added. The following constituents were then mixed in successively: 29 parts by weight of a trimethylsilyl-end-stopped poly (dimethylsiloxane) having a viscosity of 0.1 Pa * s, 9.5 parts by weight of a hydrophobic pyrogenic silica with a specific surface area of 130 m 2 / g, 0.8 part by weight of a silane with the formula H 2 NCH 2 CH 2 CH 2 Si (OC 2 H 5 ) 3 and 0.3 part by weight of a catalyst solution consisting of 65% dibutyltin-bis - (2-ethylhexanoate) and 35% toluene.

Die restliche Paste wurde in einer Schichtdicke von 2 mm 14 Tage lang bei 23 C und 50 % relativerThe remaining paste became in a layer thickness of 2 mm for 14 days at 23 C and 50% relative

Luftfeuchtigkeit ausgehärtet und in Anlehnung an DIN 53 504 geprüft:

  • Zugfestigkeit: 1,1 MPa
  • Zugspannung bei 100 % Dehnung: 0,35 MPa
  • Bruchdehnung: 400 %
Air humidity hardened and tested according to DIN 53 504:
  • Tensile strength: 1.1 MPa
  • Tensile stress at 100% elongation: 0.35 MPa
  • Elongation at break: 400%

Zur Überprüfung der Lagerfähigkeit wurde die Paste in Tuben vor dem Zutritt von Luftfeuchtigkeit geschützt. Nach drei Monaten zeigte die Paste beim Ausspritzen keinerlei Vernetzungserscheinungen, härtete aber anschließend unter dem Einfluß der Luftfeuchtigkeit zu einem Elastomer aus.To check the shelf life, the paste in tubes was protected from the ingress of atmospheric moisture. After three months, the paste showed no signs of crosslinking when sprayed out, but then hardened to an elastomer under the influence of atmospheric humidity.

Claims (2)

1. Verfahren zur Herstellung von Triorganyloxysilyl- bzw. Diorganyloxyorganosilyl-endgestoppten Poly-(diorganosiloxanen) aus a,w-Dihydroxypoly(diorganosiloxanen) und Tetraorganyloxysilanen oder Triorganyloxyorganosilanen, dadurch gekennzeichnet, daß man als Katalysatoren stark basische Alkaliverbindungen einsetzt, die man nach dem Ablauf der gewünschten Reaktion und vor dem Eintritt von produktschädigenden Umlagerungsreaktionen neutralisiert.1. A process for the preparation of triorganyloxysilyl- or diorganyloxyorganosilyl-end-stopped poly- (diorganosiloxanes) from a, w-dihydroxypoly (diorganosiloxanes) and tetraorganyloxysilanes or triorganyloxyorganosilanes, characterized in that the catalysts are strongly alkaline, and the compounds are reacted according to the basic processes desired reaction and neutralized before the start of product-damaging rearrangement reactions. 2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß man Hydroxide, Alkoholate oder Silanolate des Natriums oder des Kaliums verwendet.2. The method according to claim 1, characterized in that one uses hydroxides, alcoholates or silanolates of sodium or potassium.
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US6248854B1 (en) 1996-07-26 2001-06-19 Siemens Aktiengesellschaft Modified epoxysiloxane condensate, process for producing the same and its use as low-stress casting resins in the electronic and electrotechnical industry

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EP0468239A3 (en) 1992-04-29
CA2046963A1 (en) 1992-01-18
US5196497A (en) 1993-03-23
KR920002673A (en) 1992-02-28
JPH04226537A (en) 1992-08-17
DE4022661A1 (en) 1992-01-23
AU7928391A (en) 1992-01-23
AU645577B2 (en) 1994-01-20

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